Incubation temperature plays an important role in determining the hatchling and drives phenotypic variations in oviparous reptiles. Numerous studies have reported that incubation temperature affects many processes, including embryonic metabolism, body shape, selected body temperature, locomotor performance, tongue flicking, and predation. The variation of these traits is a potentially important indicator of fitness and most likely affects the hatchling′s fitness. In this article, we studied the effects of incubation temperature on the egg and hatchling in Strink Snake (Elaphe carinata) to assess the fitness of hatchlings incubated at two different temperatures.
We collected adults from the same population in Hunan to study the effect of incubation temperature on the egg incubation, hatchling metabolism and behavior. The eggs were incubated at two constant temperatures (24 and 28℃). Eggs were weighted and metabolism was measured at 5-day intervals. All hatchlings were applied to evaluate the response to chemical cues, respiration metabolism, selected body temperature, and so on. We measured tongue flicking, metabolism, locomotor performance, and predation of hatchlings at the body temperature of 28℃ because physiological and behavioral performances are dependent on the body temperature in reptiles.
A preliminary analysis revealed no difference between sexes of hatchlings in the examined traits, so we pooled data for sexes. All data were tested for normality (Kolmogorov-Smirnov test) and homogeneity of variances (Bartlett′s test). We used repeated-measures ANOVA, one-way ANOVA or one-way ANCOVA to analyze the corresponding data. Descriptive statistics was presented as mean ± standard error, and the significance level was set at α = 0.05.
Eggs incubated under different temperature regimes did not differ significantly in duration of incubation, hatching success and sex ratio (Table 1). All eggs gained mass during incubation because of absorption of water (Fig. 1). Mean values for final egg mass (weighed at the time point closest to hatching) differed between the two incubation temperatures (Fig. 1). The egg metabolism was positively correlated with egg mass and the incubation time in two incubation temperatures (Fig. 2). Eggs incubated at a higher temperature (28℃) produced more amount of carbon dioxide than those incubated at a lower temperature (24℃). The body mass and the carbon dioxide decreased with the increase of age after the snake hatched (Fig. 3). Hatchlings from lower temperature produced more amount of carbon dioxide than hatchlings from higher temperature did within the first five days after hatched. Hatchlings from two different incubation temperatures did not differ in selected body temperature, but hatchlings from higher temperature owned faster maximum swimming speed and more frequencies of tongue flicks than hatchlings from lower temperature (Fig. 4). There were significant effects of incubation temperature on hatchling initial feeding and hatchlings from lower temperature had not eaten within 10 minutes. Our results revealed that hatchlings of Strink Snake incubated at 28℃ had higher fitness than hatchlings at 24℃.